1. Field of the Invention
The present invention relates to a map-data distribution method in which a server sends map data to a client via a communication line and the client draws a map image based on the received map data, and relates to the client and the map distribution server using the same.
2. Description of the Related Art
Recently, electronic map data has been available on the World-Wide Web (“WWW”). For example, when a user accesses a web site providing electronic map data and specifies a desired location by inputting the latitude and the longitude thereof, a map image including the desired location is transmitted via the Internet to the user's computer (hereinafter referred to as the client) and is shown on a display of the computer.
Generally, a server at the web site providing the electronic map stores map data in a vector format. Therefore, when the client requests that the server transmit an electronic map, the server retrieves the map data including the desired location from a map database, draws a bitmap image by rendering the retrieved map data, and transmits the drawn image in the JPEG (Joint Photographic Experts Group) format, the GIF (Graphics Interexchange Format), or the like to the client.
When a segment of the map image is transmitted via a communication line using the above-described conventional map-data distribution method, the performance of the client computer and the quality of the communication line are not considered. Since the size of the map image tends to be large, transmission of the map image requires a long time.
In order to reduce the size of the transmitted map image, an alternative method can be considered in which the server transmits unmodified map data (i.e., plain vector data) to the client and the client renders the map data. Although this method can reduce the communication time between the server and the client, since the performance of the client computer is generally less than that of the server computer, the client must spend a great amount of time drawing the map image based on the vector map data.